SymR was originally labelled RyjC and is a 77nt RNA with a σ70 promoter. RyjC was found to overlap the yjiWopen reading frame on the opposite strand by 6nt, and was characterised as an antisense RNA which bound the 5' untranslated region of yjiW.[2] Further study led to the renaming of both yjiW and RyjC to SymE (SOS-induced yjiW gene with similarity to MazE) and SymR (symbiotic RNA) respectively.[1]

SymR blocks translation of SymE by antisense binding. SymE exhibits its toxicity by repressing global translation within the cell, cleaving mRNA in a similar manner to MazF, another toxin.[3] Quantitative Northern blot experiments showed that SymR RNA is present in cells at 10 times the concentration of SymE mRNA (0.02 fmol μg−1 and 0.2 fmol μg−1).[1]